The present invention relates generally to the field of food processing technology and, more particularly, to food processing for production and processing of semi-liquid food products, specifically, cottage cheese.
Traditionally cottage cheese is made in horizontal vats. After coagulation of the cheese curds, the curds are cut by a wire or blade cutters and then cooked by heating with gentle agitation. The heat is usually supplied by the direct introduction of steam into the vat or by recirculating heated whey.
The xe2x80x9cJet Cooking Systemxe2x80x9d manufactured by Stoelting Inc. is in widespread use commercially and is an example of a heat supply unit which may be used for a cottage cheese cooking process. In such a system, cooking is accomplished by continuously withdrawing whey at the top of the vat with a centrifugal pump, injecting culinary steam into the whey, and returning the heated whey to the upper part of the vat. Problems with such a system, and generally with the concept based on direct introduction of steam into the whey, include the need for utilization of expensive culinary steam which at the end of the process is wasted with the separated whey. Furthermore, direct introduction of the heating steam into the system results in a continuous addition of condensate to the curds-whey mixture in the vat. This complicates the cheese making process control in terms of maintaining acceptable process parameters such as an optimal level in the vat, physical-chemical properties of the whey and curds being cooked, and the heat and mass transfer situation in the processor.
The above-described Jet Cooking System does offer an option to the method of direct introduction of culinary steam into the product. This concept is based on utilization of an indirect heat exchanger located in the whey recirculating line. A heating medium, such as heated water or steam, is introduced into the indirect heat exchanger, and a special immersed strainer/suction tube assembly, located in the top of the vat, is used for continuous intake of circulating whey from the upper part of the whey layer in the vat. The heated whey is returned to the vat through a horizontal discharge jet pipe incorporated in the immersed strainer/suction assembly and located just below the surface of the whey along one side of the wall of the vat. A major disadvantage of this method of cheese processing is that the heat flow which is needed to cook the curd in the vat is continuously supplied to the top layer of whey rather than to the lower layer of the curd particles which tend to settle at the bottom part of the vat after cutting of the coagulum.
In order to continually expose the curd particles to the recirculating heated whey, the prior art cheese making methods provide mechanical agitating means which suspend the fragile curd in the whey. Numerous processing devices are known to the art for agitating and stirring the curd particles and whey in the vat. Problems with prior art mechanical agitating means have, however, been recognized, including the limited ability to pick up, dispense and mix the easily fragmented curd particles located at the bottom, ends, and corners of the vat.
The Verti-Stir Sanitator of the type manufactured by the Stoelting Co. is an example of prior art mechanical agitating means used in the industry. This method of agitation is based on a mechanical paddle-type device which creates a vertical stirring motion that suspends the curd particles in the upper layer of the heated whey in the vat. Because of the improved agitation of the process materials throughout the depth of the bed, the Stoelting process is quite effective for smaller vessels but becomes less efficient with increases in size due to the need to create two-dimensional horizontal movement within the vat contents in order to produce a final product having the same degree of mix consistency. Furthermore, most prior art mechanical agitating means which are used for larger vats are moved longitudinally along the length of the vat at limited speed in order to prevent damage to the delicate cottage cheese particles.
At the localized introduction of the recirculating heated whey in the vat such as with the Stoelting Jet Cooking System, the prior art mechanical agitating means, including the Stoelting Verti-Stir method, are inefficient in terms of overall mixing of the vat contents and maintaining a uniform temperature distribution in the processor. These deficiencies result in a final product having varying degrees of cooking consistency rather than the desired uniform consistency.
In the conventional cheese making vats which are heated by means of the recirculating whey system, the whey is continuously withdrawn from the upper layer of the whey in the vessel and, after being heated in the heat exchanger, is introduced back into this upper layer. This can result in a short-circuiting of the heated whey in the upper portion of the vat. This makes the cottage cheese cooking process less efficient and more difficult to control in terms of maintaining the required product temperature in the vat.
Furthermore, the conventional cheese making process suffers from another significant drawback which is related to the introduction of a higher velocity stream of recirculating heated whey into the upper portion of the vat by means of a horizontal jet pipe. In order to provide the required product heating rate in the vat, the flow rate of the recirculating heated whey, being the only source of the heat supply in the conventional system, is usually maintained relatively high. The introduction of the high velocity and highly turbulized jet stream of the heated whey into the upper portion of the conventional vat in an attempt to provide a maximum possible penetration and distribution of the hot whey into all of the upper layer of the whey/curd contents, causes a disintegration of the very fragile and easily fragmented cottage cheese curd particles in the vicinity of the jet, This results in a higher concentration of fines in the product which causes great difficulties in the system control and reduces the yield of the process.
Other prior art related to the subject matter of the invention is disclosed in the patent entitled xe2x80x9cClosed Cheese Making Vat with Recirculating Wheyxe2x80x9d, U.S. Pat. No. 4,321,860. In this system a vertical shaft is mounted for rotation within the vat, and the shaft carries a frame that extends radially outward from the shaft. A series of vertical blades are mounted on the frame. When the shaft is rotating the blades provide a stirring or agitating action. In this prior art apparatus, during the agitation of the precut curds, whey is continuously withdrawn from the upper portion of the vat and after being heated, is recirculated to the lower portion of the vat. The introduction of the recirculating heated whey into the vat is provided through a stationary inlet pipe which is incorporated into the side wall of the vat at the bottom level. When the shaft is rotated in the stirring direction the blades move the mass of curds within the vat to continually expose the curds to the recirculating whey entering the vat. The incoming jet of the whey passes upwardly through the curd to effect the primary agitation.
Despite the fact that, unlike all of the prior art known to the present inventors, the system according to U.S. Pat. No. 4,321,860 provides the heat supply to the curd by recirculating heated whey introduced into the lower portion of the vat, this method still suffers from two significant drawbacks. One of the drawbacks is the necessity to continuously move the entire mass of curds through the vat by rotating the agitator so that the incoming heated whey will contact and agitate the product being cooked. This intensive mechanical energy application provided by the pushing action of the rotating agitator blades leads to extensive fragmentation of the fragile curds thus reducing the yield of the process due to solids loss of cheese curds into the whey.
Another drawback is caused by the stationary location of the heated recirculating whey which is being introduced to the vat. This occurs because excessive velocity of the whey pumped into the lower portion of the vat can damage the curds and, accordingly, the velocity of the whey being returned to the vat is maintained at a relatively low level (lower than 150 feet per minute). The result is that there is only a very limited penetration of the entering whey jet into the moving mass of curds. The limited localized hydrodynamic agitation of the product takes place only in the vicinity of the stationary inlet means, and cannot provide efficient heating of the curds and a required uniform temperature distribution in the entire mass of contents in the vat. The above problems become even more difficult to resolve with increases in the size of the cottage cheese processing vat.
Due to advantages in the construction and operation of horizontal vats with increased capacity, the above-referenced vertical vat technology did not find an application in the cottage cheese making industry. Notwithstanding the advantages of the cheese cooking process with recirculating whey, the method disclosed in the above U.S. Pat. No. 4,321,860 cannot be utilized in horizontal vats.
The modern cottage cheese making practice has generated even more stringent operating standards and requirements for the cheese processing vats. Some of these new requirements, such as the need to process an ultra filtrated skim milk with a higher solids content and production of larger curds size at a maximum product yield, along with the need for increased capacity of the processing vessels, result in significant production difficulties.
In order to achieve the required standard of operation it would be advantageous to have a horizontal cottage cheese making vat that reduces problems associated with an inefficient heat supply and the resultant temperature gradient over the contents of the vat. It would also be advantageous to reduce these problems while also providing gentle agitation primarily by moveable jet streams of the recirculating heated whey which are introduced into the lower portion of the vat while avoiding the melting together of solid material.
The invention relates to an improved method and apparatus for cottage cheese making and, in particular, to the cooking stage of the system which takes place after cutting. As stated, for example, in the aforementioned U.S. Pat. No. 4,321,860, there are known mechanical means available for such cutting.
In accordance with this invention, the processing vat is composed of a horizontally oriented semi-cylindrical vat with two vertical end plates. A reciprocating agitating unit is mounted on a traversing carriage above the vat and includes a horizontal drive shaft that extends along the central axis of the semi-cylindrical vat. Mounted on the reversible drive shaft is a coupling and a horizontal whey distributing manifold is attached to the coupling by means of gusset plates. One or several whey discharging pipes are connected to the whey distributing manifold and they are positioned so that they are radially extended below the manifold into the semi-cylindrical volume of the vat.
The whey discharge opening of discharge pipe is located a short distance from the circumferential inner surface of the vat. This opening at the lower end of the whey discharge pipe has the configuration of a flat pattern nozzle with the longitudinal center line of the nozzle being directed preferably along the longitudinal center line of the semi-cylindrical vat.
Attached to the lower end of each whey discharge pipe directly above the whey discharge opening is an agitating (stirring) paddle which has a symmetrical configuration with two curd engaging faces positioned along the center line of the vat.
During the agitation cycle the reversible drive repeatedly rotates the agitating unit alternately clockwise and counter-clockwise so that the whey discharging pipes with the paddles attached move back and forth through a generally semicircular path in a vertical plane of the curd-filled volume of the vat. Whey is continuously withdrawn from the upper portion of the vat by the pump and, using the rotatable agitating whey discharge unit, which includes the whey distributing manifold and whey discharging pipes, the whey is re-introduced into the lower portion of the vat which is filled with curds.
The flat pattern streams of the recirculating whey discharged from the repeatedly rotatable clockwise/counter-clockwise whey discharging pipes provide gentle hydrodynamic agitation for the curds. The paddles, which are attached to the whey discharging pipes, have such an overall construction so as to provide a smooth streamlined flow around. This further contributes to the agitating efficiency of the device, minimizing the fragmentation or disintegration of the curds.
During the cheese making operation, the agitating unit is reciprocated along the length of the vat by means of a traversing carriage, for instance, a mechanical arm, thereby providing a repeated zonal agitation all over the operating volume of the vat. A flexible hose is provided to connect the stationary whey recirculating piping system with the whey distributing manifold which is installed on the mobile reciprocating-traversing carriage.
During the heating of the vat""s contents in the course of the cheese cooking cycle, the recirculating whey is heated by means of a heat exchanger which is included in the whey recirculation piping system. Therefore, the rotatable reciprocated agitating unit employed by the present invention to both gently agitate and supply heat directly into the layer of the curds provides very efficient and uniform thermal processing of cheese all over the operating volume of the vat. The invention also provides means for uniform heat distribution throughout the length of a large oblong vat and avoids the use of cumbersome complicated mechanical agitators thereby reducing the overall cost of the cheese making system and facilitating the cleaning of the apparatus after the process has been completed. By utilizing means which facilitate both gentle agitation and highly efficient heat supply by discrete streams of heated recirculated whey discharged through the mobile reciprocating nozzles, the operating conditions in the vat can be precisely controlled resulting in increased yields.